1. Field of the Invention
This invention relates to a circuit breaker having a faster acting trip unit and, more particularly, it pertains to a magnetic shunt hold back circuit in which magnetic flux lines are concentrated between a core and armature.
2. Description of the Prior Art
The circuit-interrupting art is everchanging and compact circuit breakers have evolved that comprise overcurrent protective devices, or trip units, that function in response to abnormal currents, such as overcurrents, ground fault currents, and short circuits, that occur in an electrical distribution system. Such trip units are disclosed in U.S. Pat. Nos. 3,530,414; 3,797,007; 3,808,847; 3,815,064; 3,950,716; 3,950,717; 4,074,218; and 4,313,098. Though these circuit breakers have a greater range for adjusting for specific trip currents between maximum and minimum air gaps between the magnet and the armature of the trip units, there is a need for a device that provides for faster tripping action at a predetermined overcurrent condition. This is especially true for fast acting current limiting circuit breakers.
The invention entitled "Circuit Breaker with Magnetic Shunt Hold Back Circuit", Ser. No. 858,137, filed Sept. 30, 1986, comprises means for calibrating a circuit breaker that also includes a hold-back bracket. But where the parts and assembly are provided free or substantially free of defects for required ratings, means for calibration are usually unnecessary.